In the processing of hydrocarbon fluids it is necessary to remove impurities such as carbon dioxide, water, sulfur compounds and other substances from hydrocarbon mixtures. Although various processes have been developed over the years to accomplish this, increased emphasis on less energy intensive processes is causing processes which may have been considered satisfactory in the past to be reexamined. Solvent processes utilizing amines are an example of one approach which is now perceived as requiring too much energy to operate. In addition, disposal of spent aqueous solvents presents an environmental burden.
An energy saving alternative to solvent processes and other processes for removing impurities from liquid or gaseous hydrocarbons is the use of semi-permeable membranes. The theory and use of semi-permeable membranes, also sometimes referred to in the art as permeable membranes, are well known. A feed stream of the hydrocarbon fluid to be treated is caused to contact, at elevated pressure, a membrane designed to selectively permit specific materials to pass through by diffusion. When the partial pressure of the material in question is sufficiently greater in the feed stream than on the permeate side of the membrane, permeation flux of the material to the lower partial pressure takes place. A problem arises when valuable hydrocarbons are lost in the permeate. In such cases a compressor is normally employed to capture or recycle the permeate or to repressurize the permeate for a second stage of permeation. In other cases, it is necessary to use vacuum pumps or compressors to produce sufficient driving force to effect the separation economically, or at all. Such arrangements substantially increase the capital cost of the process as well as the operating expense.
It would be beneficial to be able to eliminate the need for a compressor in the system, thereby reducing the costs mentioned above. It would also be beneficial to reduce costs by making the primary membrane smaller, without impairing the efficiency and effectiveness of the process.